1. Field of the Invention
This invention relates to an infrared imaging system, and more particularly to a solid state imaging system utilizing pyroelectric detectors in an array.
In our copending applications, Ser. Nos. 912,884 and 912.885, filed on Sept. 26, 1986, and both entitled "Gate Coupled Input Circuit," we disclose and claim alternate embodiments of the invention disclosed herein.
2. Background of the Invention
In the prior art it has been recognized that infrared imaging systems having few or no moving or fragile parts are desirable. Such infrared imaging systems should be very small because detector arrays would be fabricated on a single large scale integrated circuit chip along with associated electronics. Basically, two types of detectors are typically considered for such a solid state infrared imaging system. They are ferroelectric detectors which must be operated above the Curie temperature of the ferroelectric material, as is known in the art, and typically require that the detectors be heated. Above the Curie temperature the ferroelectric detectors have a cubic crystal structure that is very susceptible to polarization, but is not spontaneously polarized as it is below the Curie temperature. Thus, above the Curie temperature ferroelectric detectors require an external electric field in order to generate a signal. The other type of detector is a pyroelectric detector that is operated below its Curie temperature and exhibits a spontaneous dipole moment that produces an internal electric field, so an externally generated electric field is not required for these detectors to work.
In the prior art, infrared imaging systems utilizing ferroelectric detectors have been built. They have separate detector heating means and electric field biasing means for the detectors, and rows of detectors are sequentially enabled and connected to a common preamplifier. These preamplifiers are made up of a combination of integrated circuits and discrete components. The separate field biasing means and separate preamplifiers require increased space and increase the cost of the infrared imaging system.
To minimize circuit cost, a single preamplifier is used to amplify the signal from all detectors in each row of an array of detectors. With this common preamplifier arrangement the fundamental sensitivity limit for each individual detector cannot be achieved.
Other infrared detector array arrangements have been provided in the prior art that do not need to be heated, but they have another problem. They have to be cooled by a cryogenic cooler to temperatures of in the order of 77 Kelvin and below. In addition, such cryogenic cooling arrangements often utilize a bottle of a liquified gas such as nitrogen. This is bulky and the bottle must be changed frequently as the gas is used up.
Thus, there is a need in the art for an infrared imaging system having an infrared detector array that does not have to be heated or cooled (which requires power), does not require separate electric field detector biasing circuits, and does not utilize shared amplifiers.